This project is composed of two aspects: determination of the ovarian cell type which is the most sensitive to the action of the toxicant, i.e., the target cell, and then the determination of the mechanism of action of the toxicant on that particular cell. With regard to the first part, we have determined the ovarian target cell for cyclophosphamide (growing granulosa cells) and are determining the target cell for phthalate esters and glycol ethers. Mechanistically we are examining the effect of phthalate esters on granulose cell function (the target cell based on preliminary evidence) using granulosa cells cultured from DES-implanted immature rats (F-344). Mono(2-ethylhexyl)phthalate, the active metabolite of the phthalate ester di-(ethylhexyl)phthalate, inhibits FSH-stimulated cAMP accumulation in a time- and dose-dependent manner. MEHP also inhibits progesterone production, a cAMP dependent process. The action of MEHP appears to be at the level of the FSH receptor or receptor coupling to the adenylate cyclase. It does not involve activation of protein kinase C as the action of MEHP is not mimicked by phorbol esters. We are currently examining the effect of MEHP on granulosa cell ATP levels and mitochondrial function.